# Stress Tensor on Null Boundaries

## TL;DR

This paper develops a stress tensor framework on null boundaries using the Brown-York approach, enabling computation of quasi-local energy and angular momentum for gravitational solutions, with a new regularization method avoiding embedding issues.

## Contribution

It introduces a novel stress tensor on null boundaries and proposes a counterterm method to regularize energy without embedding difficulties.

## Key findings

- Successfully computed quasi-local energy and angular momentum for known solutions.
- Demonstrated a new regularization technique for null boundary energy calculations.
- Extended the Brown-York formalism to null boundaries with a counterterm approach.

## Abstract

Using the Brown-York prescription for the definition of quasilocal gravitational energy-momentum tensor on a boundary and also complete canonical structure on a null boundary which has been found recently \cite{Aghapour:2018icu}, we propose a similar stress tensor on the null boundary. Then we exploit this stress tensor to compute the quasi-local energy and angular momentum for some well-known gravitational solutions. We have found that in addition to reference spacetime method for regularizing total energy, in the case of null boundary we can add a possible counterterm so avoiding embedding difficulties.